Patterning of a composition comprising silver nanowires

ABSTRACT

The present invention relates to the production of a layer structure, comprising the following process steps:
     i) coating a substrate with a composition at least comprising silver nanowires and a solvent;   ii) at least partial removal of the solvent, thereby obtaining a substrate that is coated with an electrically conductive layer, the electrically conductive layer at least comprising the silver nanowires;   iii) bringing into contact selected areas of the electrically conductive layer with an etching composition, thereby reducing the conductivity of the electrically conductive layer in these selected areas, wherein the etching composition comprises an organic compound capable of releasing chlorine, bromine or iodine, a compound containing hypochloride, a compound containing hypo-bromide or a mixture of at least two of these compounds.   

     The invention also relates to a layer structure obtainable by this method, a layer structure, the use of a layer structure, an electronic component and the use of an organic compound.

This application is the national stage of International PatentApplication No. PCT/EP2014/001963, filed Jul. 18, 2014, which claims thebenefit of European Patent Application No. 13003674.2, filed Jul. 22,2013, which is hereby incorporated by reference in its entirety.

The present invention relates to a method for producing a layerstructure, a layer structure obtainable by this method, a layerstructure, the use of a layer structure, an electronic component and theuse of an organic compound.

The production of metal nanowires and in particular silver nanowires viathe polyol process is well known and, for example, disclosed in DE-A-102010 017706, U.S. Pat. No. 7,585,349 and WO-A-2008/073143. A Polyol isused as solvent and as a reduction agent for silver salts, mostprominently silver nitrate, whilst a dispersion agent such aspolyvinylpyrrolidone and a halide are present. The components are chosenin such a manner that anisotropic wires are formed with an aspect ratioof 10:1 up to 1000:1 or more.

The deposition of the silver nanowires onto a substrate leads toelectrically conductive films with low sheet resistance and hightransparency. These can be deposited on glass as well as flexiblesubstrates. Hence, silver nanowires are an alternative to establishedtransparent conductors such as ITO (=indium tin oxide layers).

There is a great need to be able to pattern electrically conductivelayers (including those based on silver nanowires) in a similar way toITO layers, “patterning” referring here and hereafter to any measurewhich in a sub-area or in multiple subareas of the electricallyconductive layers leads to an at least partial reduction and preferablyto a complete elimination of the conductivity.

One possibility for producing patterned layers based on silver nanowiresis to apply these structures onto a surface in a patterned way by meansof certain printing methods. In addition to the use of printing pastes,another possibility for producing patterned coatings from silvernanowires is first to produce a uniform, unpatterned coating of silvernanowires and to pattern it subsequently by washing the coated substratewith water, thereby removing silver nanowires from the respective areas.As a result, a patterned structure is obtained which in some areas arecoated with silver nanowires and which in some areas is free of anycoating. As the silver nanowire coating has in influence on the opticalproperties, removal of this coating in certain areas leads toinhomogeneous optical properties within the patterned structure, whichin most applications, such as in touch screens, is not desirable.

WO-A-2011/106438 describes a process for the deposition and structuringof silver nanowires. Silver nanowires are deposited from an aqueousdispersion and the resulting layers can subsequently be etched using andetching solution that comprises a halide, such as chloride or iodide,and an oxidizer, such as FeCl₃, CuCl₂, HNO₃, H₂O₂ or O₂. The etchingsolutions used in the Examples of WO-A-2011/106438 further comprisedoxidizing agents such as KMnO4. The resulting etched film shows anincrease in sheet resistances compared to the non-etched areas withlittle or no change in sheet resistance. The disadvantage of thisprocess, however, is that the etching substances such as FeCl₃, CuCl₂,HNO₃, H₂O₂ or KMnO₄ critically compromise the colour of the coating,which has an adverse influence on the external appearance of thecoating.

US-A-2012/0104374 describes compositions containing PEDOT:PSS and silvernanowires that can be used for the preparation of highly transparent andhighly conductive films. The presence of a polymer leads to thesmoothing of the resulting films. However, no structuring method isavailable for such mixtures.

The object of the present invention was to overcome the disadvantagesarising from the prior art in connection with the patterning ofelectrically conductive layers based on silver nanowires.

In particular, the object of the present invention was to provide amethod for patterning electrically conductive layers based on silvernanowires, in which—compared to the concepts known from the priorart—significant differences in the sheet resistance can be achievedbetween etched and non-etched areas without effecting the opticalappearance of the patterning. In particular, the process should allowthe production of transparent and structured electrically conductivelayers, in which some areas (i. e. the non-etched areas) arecharacterized by a surface resistance of preferably not more than 250Ω/square, and in which other areas (i. e. the etched areas) arecharacterized by a surface resistance of at least 1×10⁶ Ω/square andwherein the colour difference between these areas is as low as possible.

A contribution to achieving these objects is made by a method forproducing a layer structure, comprising the process steps:

-   i) coating a substrate with a composition at least comprising silver    nanowires and a solvent;-   ii) at least partial removal of the solvent, thereby obtaining a    substrate that is coated with an electrically conductive layer, the    electrically conductive layer at least comprising the silver    nanowires;-   iii) bringing into contact selected areas of the electrically    conductive layer with an etching composition, thereby reducing the    conductivity of the electrically conductive layer in these selected    areas, wherein the etching composition comprises an organic compound    capable of releasing chlorine, bromine or iodine, a compound    containing hypochloride, a compound containing hypobromide or a    mixture of at least two of these compounds.

Completely surprisingly, but no less advantageously for that, it wasfound that if a coating that comprises silver nanowires is etched withan organic compound capable of releasing chlorine, bromine or iodine, acompound containing hypochloride, a compound containing hypobromide or amixture of at least two of these compounds, a patterned structure can beobtained that is not only characterized by a significant difference inthe surface resistance between the etched and the non-etched surfaces,but also by a very homogeneous optical appearance.

In process step i) a substrate is coated with a composition at leastcomprising silver nanowires and a solvent.

The wording “coating a substrate with a composition at least comprisingsilver nanowires and a solvent” encompasses both a process step in whichthe composition is applied directly onto the substrate and also processsteps in which the composition is applied to an interlayer that may becoated onto the substrate.

Plastic films in particular are preferred as the substrate in thisconnection, most particularly preferably transparent plastic films,which conventionally have a thickness in a range from 5 to 5000 μm,particularly preferably in a range from 10 to 2500 μm and mostpreferably in a range from 25 to 1000 μm. Such plastic films can bebased, for example, on polymers such as polycarbonates, polyesters suchas for example PET and PEN (polyethylene terephthalate and polyethylenenaphthalene dicarboxylate), copolycarbonates, polysulphones, polyethersulphones (PES), polyimides, polyamides, polyethylene, polypropylene orcyclic polyolefins or cyclic olefin copolymers (COC), polyvinylchloride, polystyrene, hydrogenated styrene polymers or hydrogenatedstyrene copolymers. In addition to plastic materials, substrates basedin particular on metals or metal oxides are also suitable as substrates,such as for example ITO layers (indium tin oxide layers) or the like.Glass is also preferred as a substrate.

This substrate is coated with a composition at least comprising silvernanowires and a solvent. The surface of the substrates can bepre-treated prior to applying the composition, for example by treatmentwith a primer, by corona treatment, flame treatment, fluorination orplasma treatment, to improve the polarity of the surface and hence thewettability and chemical affinity.

Preferred silver nanowires in the composition used in process step i)have a length of from 1 μm to 200 μm, a diameter of from 20 nm to 1300nm and an aspect ratio (length/diameter) of at least 5.

The silver nanowires in the composition used in process step i) can beprepared by known methods in the art. In particular, silver nanowirescan be synthesized through solution-phase reduction of a silver salt(e.g., silver nitrate) in the presence of a polyol (e.g., ethyleneglycol) and poly(vinyl pyrrolidone). Large-scale production of silvernanowires of uniform size can be prepared according to the methodsdescribed in e.g., Xia, Y. et al., Chem. Mater. (2002), 14, 4736-4745,and Xia, Y. et al., Nanoletters (2003) 3(7), 955-960.

According to a preferred embodiment of the silver nanowires used inprocess step i) these nanowires are produced with the process disclosedin DE-A-10 2010 017 706. This process comprises the steps:

-   a) provision of a reaction mixture comprising    -   a polyol,    -   an organic chemical which is adsorbed on to a silver surface,    -   a chemical which forms a halide and/or one which forms a        pseudohalide, wherein the chemical which forms a halide is a        salt of one of the halides Cl⁻, Br⁻ and/or I⁻ and wherein the        chemical which forms a pseudohalide is a salt of one of the        pseudohalides SCN⁻, CN⁻, OCN⁻ and/or CNO⁻,    -   a chemical which forms a redox pair, chosen from the group        consisting of bromine, iodine, vanadium and mixtures thereof,        and    -   a silver salt, preferably in an amount of at least 0.5 wt. %,        based on the total weight of the reaction mixture,-   b) heating of the reaction mixture to a temperature of at least    100° C. for the duration of the reaction.

Preferred embodiments of this process for the production of silvernanowires are those embodiments which in DE-A-10 2010 017 706 aredescribed as preferred embodiments. In this context, it is particularlypreferred that

-   -   the polyol is preferably selected from the group consisting of        ethylene glycol, tetraethylene glycol, 1,2-propanediol,        dipropylene glycol, 1,2-butanediol, 1,3-butanediol,        1,4-butanediol and 2,3-butanediol;    -   the organic chemical which is adsorbed on to a silver surface is        preferably selected from the group consisting of        polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA) and of        various grades (molecular weights) and copolymers of these        polymers.

According to a preferred embodiment of the process according to thepresent invention the composition used in process step i) furthercomprises a sulphonated polymer.

The sulfonated polymers in the composition used in process step i) canbe any polymer that comprises sulfonic acid groups or sulfonate groups.Preferred sulfonated polymers comprise sulphonated polyether etherketones (sPEEK), preferably those disclosed in WO-A-2011/113612, orpolymers having a polyalkylene-backbone and bearing sulfonic acid groupsor sulfonate groups.

Preferred polymers having a polyalkylene-backbone and bearing sulfonicacid groups or sulfonate groups can be obtained by sulfonation ofpolymers having a polyalkylene-backbone, such as polystyrene, or bypolymerisation of ethylenically unsaturated monomers bearing sulfonicacid groups (or salts thereof), optionally together with ethylenicallyunsaturated monomers that do not bear a sulfonic acid groups (orsulfonate groups). Examples of ethylenically unsaturated monomersbearing a sulfonic acid group or a sulfonate group are substituted orunsubstituted ethylenesulfonic acid compounds such as vinylsulfonicacid, vinylsulfonic acid salt, allylsulfonic acid, allylsulfonic acidsalt, methallylsulfonic acid, methallylsulfonic acid salt, 4-sulfobutylmethacrylate, 4-sulfobutyl methacrylate salt,methallyloxybenzenesulfonic acid, methallyloxybenzenesulfonic acid salt,allyloxybenzenesulfonic acid and allyloxybenzenesulfonic acid salt,substituted or unsubstituted styrenesulfonic acid compounds such asstyrenesulfonic acid, styrenesulfonic acid salt, -methylstyrenesulfonicacid and methylstyrenesulfonic acid salt, substituted acrylamidesulfonicacid compounds such as acrylamide-t-butylsulfonic acid,acrylamide-t-butylsulfonic acid salt,2-acrylamide-2-methylpropanesulfonic acid and2-acrylamide-2-methylpropane-sulfonic acid salt, substituted orunsubstituted cyclovinylenesulfonic acid compounds such ascyclobutene-3-sulfonic acid and cyclobutene-3-sulfonic acid salt andsubstituted or unsubstituted butadienesulfonic acid compounds such asisoprenesulfonic acid, isoprenesulfonic acid salt,1,3-butadiene-1-sulfonic acid, 1,3-butadiene-1-sulfonic acid salt,1-methyl-1,3-butadiene-2-sulfonic acid,1-methyl-1,3-butadiene-3-sulfonic acid salt,1-methyl-1,3-butadiene-4-sulfonic acid and1-methyl-1,3-butadiene-4-sulfonic acid salt.

These monomers bearing a sulfonic acid group or a sulfonate group can,for example, be copolymerized with monomers such as ethylene, propene,1-butene, 2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, styrene,p-methylstyrene, p-ethylstyrene, p-butylstyrene, 2,4,6-trimethylstyrene,p-methoxystyrene, 2-vinylnaphthalene, 6-methyl-2-vinyl-naphthalene,1-vinylimidazole, vinylpyridine, vinyl acetate, acrylaldehyde,acrylonitrile, N-vinyl-2-pyrrolidone, acrylamide,N,N-dimethylacrylamide, methyl acrylate, ethyl acrylate, propylacrylate, butyl acrylate, isobutyl acrylate, isooctyl acrylate,isononylbutyl acrylate, allyl acrylate, ethyl methacrylate, hydroxyethylacrylate, methoxyethyl acrylate, methoxybutyl acrylate, stearylacrylate, acrylic acid ester, acryloyl morpholine, vinylamine,N,N-dimethylvinylamine, N,N-diethylvinylamine, N,N-dibutylvinylamine,N,N-di-t-butylvinylamine, N,N-diphenylvinylamine, N-vinyl carbazole,vinyl alcohol, vinyl chloride, vinyl fluoride, vinyl ether,cyclopropene, cyclobutene, cyclopentene, cyclohexene, cycloheptene,cyclooctene, 2-methylcyclohexene, vinylphenol, 1,3-butadiene,1-methyl-1,3-butadiene, 2-methyl-1,3-butadiene,1,4-dimethyl-1,3-butadiene, 1,2-dimethyl-1,3-butadiene,1,3-dimethyl-1,3-butadiene, 1-octyl-1,3-butadiene,2-octyl-1,3-butadiene, 1-phenyl-1,3-butadiene, 2-phenyl-1,3-butadiene,1-hydroxy-1,3-butadiene, 2-hydroxy-1,3-butadiene, allyl acrylate,acrylamideallyl, divinyl ether, o-divinylbenzene, m-divinylbenzene andp-divinylbenzene.

Particularly preferred sulfonated polymers are polystyrenesulfonic acid(PSS) as well as copolymers of styrene and styrenesulfonic acid with asulfonation degree of at least 50%, preferably at least 75% and evenmore preferred at least 100%, wherein the use of polystyrenesulfonicacid is mostly preferred.

The molecular weight (M_(w)) of the sulfonated polymer, preferablypolystyrenesulfonic acid, is preferably 1000 to 2000000, particularlypreferably 2000 to 500000. The molecular weight is determined by gelpermeation chromatography using polystyrene sulphonic acids of definedmolecular weights as the calibration standard. The polyacids or alkalisalts thereof are available commercially, for example polystyrenesulphonic acids and polyacrylic acids, or can be produced by knownmethods (see for example Houben Weyl, Methoden der organischen Chemie,Vol. E 20 Makromolekulare Stoffe, Part 2, (1987), p. 1141 ff.).

The weight ratio of silver nanowires to sulfonated polymer (silvernanowire:sulfonated polymer) in the composition used in process step i)is preferably in the range from 50:1 to 1:50, more preferably in therange from 25:1 to 1:25 and most preferably in the range from 10:1 to1:10. The concentration of the sulfonate polymer in the composition thatis used in process step i) is preferably in the range from 0.1 to 10wt.-%, more preferably in the range from 0.2 to 4 wt.-%.

The solvent in the composition used in process step i) can be water, anorganic solvent such as methanol, ethanol, 1-propanol or 2-propanol, ora mixture or water and one of these organic solvents, wherein the use ofwater as a solvent is particularly preferred. The composition used inprocess step i) may also comprise a certain residue of solvents thathave been used for the preparation of the silver nanowires.

According to a particularly preferred embodiment of the processaccording to the present invention the composition used in process stepi) not only comprises a sulphonated polymer as a further component, butalso a conductive polymer such as a polythiophene, a polypyrrole or apolyaniline, wherein a polythiophene is particularly preferred.

Preferred polythiophenes are those of the formula (I)

in which

-   R¹ and R² independently of each other each denote H, an optionally    substituted C₁-C₁₈ alkyl radical or an optionally substituted C₁-C₁₈    alkoxy radical, R₁ and R₂ together denote an optionally substituted    C₁-C₈ alkylene radical, wherein one or more C atoms can be replaced    by one or more identical or different heteroatoms selected from O or    S, preferably a C₁-C₈ dioxyalkylene radical, an optionally    substituted C₁-C₈ oxythiaalkylene radical or an optionally    substituted C₁-C₈ dithiaalkylene radical, or an optionally    substituted C₁-C₈ alkylidene radical, wherein optionally at least    one C atom is replaced by a heteroatom selected from O or S.

In a particularly preferred embodiment of the method according to theinvention polythiophenes are preferred which comprise repeating units ofthe general formula (I-a) and/or the general formula (I-b):

In the context of the invention the prefix “poly” is understood to meanthat more than one identical or different repeating unit is comprised inthe polythiophene. The polythiophenes comprise in total n repeatingunits of the general formula (I), wherein n can be a whole number from 2to 2000, preferably 2 to 100. The repeating units of the general formula(I) within a polythiophene can in each case be identical or different.Polythiophenes comprising in each case identical repeating units of thegeneral formula (I) are preferred.

The polythiophenes preferably each bear H at the end groups.

In particularly preferred embodiments the polythiophene ispoly(3,4-ethylene-dioxythiophene) (PEDOT),poly(3,4-ethyleneoxythiathiophene) or poly(thieno-[3,4-b]thiophene,whereby poly(3,4-ethylenedioxythiophene) is most preferred.

The polythiophenes are preferably cationic, wherein “cationic” relatesonly to the charges located on the polythiophene main chain. Dependingon the substituent at the radicals R¹ and R², the polythiophenes canbear positive and negative charges in the structural unit, the positivecharges being located on the polythiophene main chain and the negativecharges optionally at the radicals R substituted with sulphonate orcarboxylate groups.

The positive charges of the polythiophene main chain can be partially orcompletely saturated by the optionally present anionic groups at theradicals R¹ and R². Considered as a whole, the polythiophenes can becationic, neutral or even anionic in these cases. Nevertheless, in thecontext of the invention they are all considered as cationicpolythiophenes, since the positive charges on the polythiophene mainchain are decisive. The positive charges are not represented in theformulae because they are mesomerically delocalised. However, the numberof positive charges is at least 1 and at most n, where n is the totalnumber of all repeating units (identical or different) within thepolythiophene.

It is, however, particularly preferable according to the presentinvention for the positive charges on the polythiophene main chain to becompensated by the sulfonate groups of the sulfonated polymer. In thiscontext it is particularly preferred that the conductive polymer ispresent in the form of a complex formed from the polythiophene and thesulfonated polymer, wherein it is most preferred that the conductivepolymer is poly(3,4-ethylenedioxythiophene) (PEDOT), that the sulfonatedpolymer is polystyrenesulfonic acid and that these components arepresent in the form of a PEDOT/PSS-complex. Such a PEDOT/PSS-complexcan, for example, be obtained by oxidatively polymerizing3,4-ethyenedioxythiophene in the presence of polystyrenesulfonic acid,as described in detail in chapter 9 of Elschner et al.: “PEDOTPrinciples and Applications of an Intrinsically Conductive Polymer”, CRCPres s (2011).

The weight ratio of polythiophene to the sulfonated polymer, preferablythe weight ratio of PEDOT to PSS (PEDOT:PSS), in these complexes ispreferably in a range from 1:0.3 to 1:100, preferably in a range from1:1 to 1:40, particularly preferably in a range from 1:2 to 1:20 andextremely preferably in a range from 1:2 to 1:15.

The composition used in process step i) may further comprise additives.Suitable additives are, for example, compounds which raise theconductivity, such as for example ether group-comprising compounds suchas for example tetrahydrofuran, lactone group-comprising compounds suchas butyrolactone, valerolactone, amide group- or lactam group-comprisingcompounds such as caprolactam, N-methyl caprolactam, N,N-dimethylacetamide, N-methyl acetamide, N,N-dimethyl formamide (DMF), N-methylformamide, N-methyl formanilide, N-methyl pyrrolidone (NMP), N-octylpyrrolidone, pyrrolidone, sulphones and sulphoxides, such as for examplesulpholane (tetramethylene sulphone), dimethyl sulphoxide

(DMSO), sugar or sugar derivatives, such as for example sucrose,glucose, fructose, lactose, sugar alcohols such as for example sorbitol,mannitol, furan derivatives such as for example 2-furan carboxylic acid,3-furan carboxylic acid, and/or di- or polyalcohols such as for exampleethylene glycol, glycerol or di- or triethylene glycol. Tetrahydrofuran,N-methyl formamide, N-methyl pyrrolidone, ethylene glycol, dimethylsulphoxide or sorbitol are particularly preferably used asconductivity-raising additives.

One or more binders, such as polyvinyl acetate, polycarbonate, polyvinylbutyral, polyacrylic acid esters, polyacrylic acid amides,polymethacrylic acid esters, polymethacrylic acid amides, polystyrene,polyacrylonitrile, polyvinyl chloride, polyvinyl pyrrolidones,polybutadiene, polyisoprene, polyethers, polyesters, polyurethanes,polyamides, polyimides, polysulphones, silicones, epoxy resins,styrene/acrylate copolymers, vinyl acetate/acrylate copolymers andethylene/vinyl acetate copolymers, polyvinyl alcohols or celluloses, canalso be added as an additive to the composition. The proportion of thepolymeric binder, if used, is conventionally in a range from 0.1 to 90wt.-%, preferably 0.5 to 30 wt.-% and most particularly preferably 0.5to 10 wt.-%, relative to the total weight of the composition.

Bases or acids, for example, can be added as an additive to thecompositions to adjust the pH. In this context compounds which do notadversely affect the film forming of the dispersions are preferred, suchas for example the bases 2-(dimethylamino)ethanol, 2,2′-iminodiethanolor 2,2′,2″-nitrilotriethanol.

Furthermore, surface-active agents, such as anionic surfactants, e.g.alkylphenylsulphonic acids and salts, parafinsulphonates,alcoholsulphonates, ethersulphonates, sulphosuccinates, phosphateesters,alkylethercarboxylic acids or carboxylates, cationic surfactants, e.g.quaternary alkylammonium salts, non-ionic surfactants, e.g. linearalcohol ethoxylates, oxoalcoholethoxylates, alkylphenolethoxylate oralkylpolyglucosides may be used as additives.

The composition that is used in process step i) of the preferredembodiment of the process according to the present invention (i. e. theembodiment in which the composition that is used in process step i)further comprises a sulphonated polymer) can be obtained by simplymixing together the silver nanowires, preferably in the form of adispersion obtained by the process disclosed in DE-A10 2010 017 706,with the sulfonated polymer, which can also be present in the form of asolution or dispersion. If the sulfonated polymer is applied in the formof a complex with an electrically conductive polymer as described above,the composition that is used in process step i) can be obtained bysimply mixing together a dispersion comprising the silver nanowires anda dispersion comprising these complexes, preferably aPEDOT/PSS-dispersion such as Clevios PH 1000.

The composition used in process step i) can be applied to the substrateby known methods, for example by spin coating, dipping, pouring,dropping on, injecting, spraying, knife application, spreading orprinting, for example inkjet, screen, intaglio, offset or pad printing,in a wet film thickness of 0.5 μm to 250 μm, preferably in a wet filmthickness of 2 μm to 50 μm.

In process step ii) of the process according to the present invention atleast part of the solvent is removed, thereby obtaining a substrate thatis coated with an electrically conductive layer, the electricallyconductive layer at least comprising the silver nanowires and—if thecomposition used in process step i) further comprises a sulfonatedpolymer—the sulphonated polymer, said removal preferably being performedby simple evaporation.

The thickness of the electrically conductive layer obtained in processstep ii) is preferably 1 nm to 50 μm, particularly preferably in a rangefrom 1 nm to 5 μm and most preferably in a range from 10 nm to 500 nm

In process step iii) of the of the process according to the presentinvention selected areas of the electrically conductive layer arebrought into contact with an etching composition, thereby reducing theconductivity of the electrically conductive layer in these selectedareas.

According to a preferred embodiment of the process according to thepresent invention the etching composition comprises an organic compoundcapable of releasing chlorine, bromine or iodine, a compound containinghypochloride, such as sodium hypochloride or potassium hypochloride, acompound containing hypobromide, such as sodium hypobromide or potassiumhypobromide, or a mixture of at least two of these compounds. Thesecompounds are subsequently called “etching compounds”.

The formulation “which is capable of releasing chlorine, bromine oriodine” is preferably understood according to the present invention asmeaning an on organic compound, which, after addition of a solvent,preferably after addition of water, releases chlorine in the form ofCl₂, HOCl, OCl⁻ or a mixture of at least two of these chlorinecompounds, or bromine in the form of Br₂, HOBr, OBr⁻ or a mixture of atleast two of these bromine compounds, or iodine in the form of I₂, HIO,IO⁻ or a mixture of at least two of these iodine compounds.

An organic compound capable of releasing chlorine, bromine or iodinethat is particularly preferred according to the invention is an organiccompound comprising at least one structural element (II)

in which

-   -   Hal is a halogen selected from the group consisting of chlorine,        bromine or iodine, but preferably denotes chlorine or bromine,    -   Y is selected from N, S and P, but preferably denotes N, and    -   X₁ and X₂ can be the same or different and each denote a        halogen, preferably chlorine or bromine, a carbon atom or a        sulphur atom, wherein one or more further atoms can optionally        be bonded to X₁ and X₂. The number of further atoms bonded to X₁        and X₂ is dependent on the covalence of X₁ and X₂.

According to a first particular embodiment of the method according tothe invention the organic compound capable of releasing chlorine orbromine comprises at least two structural elements (III) in which Haldenotes a chlorine atom or a bromine atom and Y denotes nitrogen,wherein these at least two structural elements (III) can optionally alsobe different from one another. In this connection it is mostparticularly preferable according to a first variant of the method forthe organic compound capable of releasing chlorine or bromine tocomprise the structural element (III)

in which a chlorine atom or a bromine atom is bonded to at least two ofthe nitrogen atoms. Of these organic compounds, sodiumdichlorodiisocyanurate, sodium dibromodiisocyanurate,tribromoisocyanuric acid and trichloroisocyanuric acid are particularlypreferred.

According to a second method variant of this first particular embodimentof the method according to the invention it is preferable for theorganic compound capable of releasing chlorine or bromine to comprisethe structural element (IV)

in which a chlorine atom or a bromine atom is bonded to the two nitrogenatoms and in which R³ and R⁴ can be the same or different and denote ahydrogen atom or a C₁-C₄ alkyl group, in particular a methyl group or anethyl group.

In this connection particularly preferred organic compounds capable ofreleasing chlorine or bromine are selected from the group consisting ofbromo-3-chloro-5,5-dimethylhydantoin,1-chloro-3-bromo-5,5-dimethylhydantoin,1,3-dichloro-5,5-dimethylhydantoin and1,3-dibromo-5,5-dimethylhydantoin.

According to a second particular embodiment of the method according tothe invention the organic compound capable of releasing chlorine orbromine comprises exactly one structural element (II). In this case tooY preferably denotes N.

According to a first method variant of this second particular embodimentof the method according to the invention the organic compound capable ofreleasing chlorine or bromine is N-chlorosuccinimide orN-bromosuccinimide.

According to a second method variant of this second particularembodiment of the method according to the invention the organic compoundcapable of releasing chlorine or bromine comprises the structuralelement (V)

in which a chlorine atom or a bromine atom is bonded to the nitrogenatom and in which R⁵, R⁶, R⁷ and R⁸ can be the same or different anddenote a hydrogen atom or a C₁-C₄ alkyl group, which can optionally besubstituted with bromine or chlorine. In this connection3-bromo-5-chloromethyl-2-oxazolidinone,3-chloro-5-chloromethyl-2-oxazolidinone,3-bromo-5-bromomethyl-2-oxazolidinone and3-chloro-5-bromomethyl-2-oxazolidinone can be cited as examples ofsuitable organic compounds.

Furthermore, the organic compound capable of releasing chlorine orbromine according to the second particular embodiment of the methodaccording to the invention can for example be halazone, anN,N-dichlorosulphonamide, an N-chloro-N-alkylsulphonamide or anN-bromo-N-alkylsulphonamide in which the alkyl group is a C₁-C₄ alkylgroup, particularly preferably a methyl group or an ethyl group.

Also suitable as the organic etching compound capable of releasingchlorine, bromine or iodine according to a third particular embodimentof the method according to the invention are organic compounds selectedfrom the group consisting of 5-chloro-2-methyl-4-isothiazolin-3-one,4,5-dichloro-2-N-octyl-4-isothia-zolin-3-one,bromo-2-nitro-1,3-propanediol (BNPD), 2,2-dibromo-3-nitrilopropionamide,dibromonitroethyl propionate, dibromonitroethyl formate,sodium-N-chloro-(4-methylbenzene)sulphonamide or tetraglycinehydroperiodide.

The etching composition used in process step iii) is preferably anaqueous solution or dispersion in which the etching compound isdissolved or dispersed. In this connection it is particularly preferablefor the aqueous solution or dispersion to have a pH determined at 25° C.in the range from 1 to 12.

The etching composition, particularly preferably the aqueous solution ordispercion, preferably comprises the etching compound in a concentrationin a range from 0.1 to 50 wt.-%, particularly preferably in a range from0.5 to 35 wt.-% and most preferably in a range from 1 to 20 wt.-%,relative in each case to the total weight of the etching composition.

The bringing into contact of the electrically conductive layer with theetching composition in process step iii) preferably takes place bydipping the electrically conductive layer into the etching compositionor by printing the electrically conductive layer with the etchingcomposition. To ensure an adequate patterning, the electricallyconductive layer remains in contact with the etching composition,preferably the aqueous solution or dispersion, for approximately 1second to 30 minutes, particularly preferably for approximately 30seconds to 15 minutes and most preferably approximately 1 to 5 minutes,before it is withdrawn again or before the etching composition isremoved again. The temperature of the etching composition during thebringing into contact with the electrically conductive layer ispreferably in a range from 10 to 40° C., particularly preferably in arange from 20 to 30° C., whereby the use of an etching composition atroom temperature (25° C.) is most preferred.

Various methods are suitable for bringing only a part of theelectrically conductive layer of the layer structure into contact withthe etching composition for the purpose of patterning. In the simplestcase a patterning can be achieved by dipping only a part of the layerstructure into the etching composition and correspondingly also bringingonly a part of the electrically conductive layer into contact with theetching composition. It is, however, also conceivable for the etchingcomposition to be applied by, for example, printing on only certainareas of the electrically conductive layer on the layer structure. Theuse of templates with which the layer structures can be covered andwhich have cut-outs through which the etching composition can come intocontact with certain areas of the electrically conductive layer is alsoconceivable. It is moreover also possible to use photolithography tobring about a patterning.

The method according to the invention can comprise as a further processstep:

-   iv) washing the electrically conductive layer brought into contact    with the etching composition,    wherein washing preferably takes place by dipping the layer    structure into a solvent, for example water, and this can be    followed by a drying step.

In the method according to the invention it is furthermore preferablefor the bringing into contact of the electrically conductive layer withthe etching composition to take place under conditions such that thediameter of the silver nano wires in the electrically conductive layerin the areas brought into contact with the etching composition isreduced by at most 50%, particularly preferably by at most 25% and mostpreferably by at most 10%.

A contribution to achieving the objects set out in the introduction isalso made by a layer structure obtainable by the method according to thepresent invention described above.

A contribution to achieving the objects set out in the introduction isalso made by a layer structure comprising a substrate and anelectrically conductive layer on top the substrate, wherein theelectrically conductive layer at least comprises silver nanowires,wherein the layer structure comprises

-   A) at least one area A in which the electrically conductive layer on    top of the substrate has a surface resistance R;-   B) at least one area B in which the electrically conductive layer on    the substrate has a surface resistance which at least 10 times,    preferably at least 100 times, still more preferably at least 1000    times, still more preferably at least 10,000 times and most    preferably at least 100,000 times greater than R,    wherein the colour difference ΔE_(area A, area B) is at most 4.5,    particularly preferably at most 3.0 and most preferably at most 1.5.    The colour difference ΔE_(area A, area B) is calculated as follows:

${\Delta\; E_{{{area}\mspace{14mu} A},{{area}\mspace{14mu} B}}} = \sqrt{\left( {L_{{area}\mspace{14mu} A}^{*} - L_{{area}\mspace{14mu} B}^{*}} \right)^{2} + \left( {a_{{area}\mspace{14mu} A}^{*} - a_{{area}\mspace{14mu} B}^{*}} \right)^{2} + \left( {b_{{area}\mspace{14mu} A}^{*} - b_{{area}\mspace{14mu} B}^{*}} \right)^{2}}$L*_(area A), a*_(area A) and b*_(area A) are the L, a and b valuesrespectively of the L*a*b* colour space of areas A and L*_(area B),a*_(area B) and b*_(area B) are the L, a and b values respectively ofthe L*a*b* colour space of areas B.

Preferred substrates and silver nanowires are those substrates andsilver nanowires that have already been mentioned in connection with theabove described process according to the present invention. Thethickness of the electrically conductive layer also preferablycorresponds to the thickness of the electrically conductive layerdescribed above as the preferred film thickness in connection with themethod according to the invention.

According to a preferred embodiment of the layer structure according tothe present invention the electrically conductive layer furthercomprises a sulphonated polymer, wherein those sulphonated polymer arepreferred that have already been mentioned in connection with the abovedescribed process according to the present invention. Furthermore, theelectrically conductive layer in the layer structure according to thepresent invention may further comprise an electrically conductivepolymer, preferably poly(3,4-ethylenedioxythiophene), which—as describedabove in connection with the process according to the presentinvention—preferably is present in the form of a complex with thesulfonated polymer, preferably in the form of a PEDOT/PSS-complex.

It is furthermore preferable in connection with the layer structureaccording to the invention for the areas A and B to have a geometricshape, preferably a geometric shape selected from the group consistingof a circle, a rectangle or a triangle. In this connection it isparticularly preferable for the areas A and B together to form a circuitdesign. In this connection it is furthermore preferable for the areas Aand B each to have a surface area of at least 0.00001 mm², preferably atleast 0.0001 mm², still more preferably at least 0.001 mm², still morepreferably at least 0.01 mm², still more preferably at least 0.1 mm²,still more preferably at least 1 mm² and most preferably at least 10mm².

A contribution to achieving the objects set out in the introduction isalso made by the use of a layer structure obtainable by the methodaccording to the invention or of a layer structure according to theinvention to produce electronic components, in particular organiclight-emitting diodes, organic solar cells or capacitors, to producetouch panels or touch screens or to produce an antistatic coating.

A contribution to achieving the objects set out in the introduction isalso made by electronic components, such as organic light-emittingdiodes, organic solar cells or capacitors or by a touch panel or a touchscreen comprising a layer structure obtainable by the method accordingto the invention or a layer structure according to the invention.

A contribution to achieving the objects set out in the introduction isalso made by the use of an organic compound capable of releasingchlorine, bromine or iodine, of a compound containing hypochloride, of acompound containing hypobromide or of a mixture at least two of thesecompounds to treat an electrically conductive layer at least comprisingsilver nanowires, preferably at least comprising silver nanowires and asulphonated polymer, more preferably at least comprising silvernanowires and a PEDOT/PSS-complex. The organic compounds alreadymentioned above as preferred organic compounds in connection with themethod according to the invention are preferred as the organic compoundcapable of releasing chlorine, bromine or iodine, as the compoundcontaining hypochloride or as the compound containing hypobromide.

The invention is now described in more detail by reference to figures,test methods and non-limiting examples.

FIG. 1 shows a cross-section of the structure of a layer structure 1according to the invention, for example an antistatic film, in generalform. On a substrate 2 a coating is applied which encompasses areas 3with a surface resistance R and areas 4 with a surface resistance atleast 10 times greater than R. FIG. 2 shows the same layer structure 1from above.

TEST METHODS

Determining the Surface Resistance

The determination was carried out by means of a so called four-pointprobe measurement as described for instance in U.S. Pat. No. 6,943,571B1. The values are given in Ω/square.

Determining the Colour Values L, a and b and the Transmission

The measurement of the transmission spectra of the coated PET films iscarried out on a Lambda 900 two-channel spectrophotometer from PerkinElmer. The instrument is fitted with a 15-cm photometer sphere,measurements are carried out in the sphere, to ensure that nointerferences of the scattered light are detected. So the here presentedvalues for transmission include also the scattered light or to this endtransmission is 1-absorption.

Spectra were recorded in the visible range of the spectra from 320 nm to780 nm in 5 nm steps. There is no sample in the reference beam, so thespectra are recorded against air.

First transmission of an uncoated substrate is measured as a reference,as a substrate Melinex 506 films with a film thickness of 175 μm areused. Subsequently the coated substrates were measured.

From the spectra, the standard colour value Y (brightness) of the samplewas calculated according to DIN 5033, on the basis of a 10°-abserver andthe light type D65. The internal transmission was calculated from theration of brightness of the substrate with the coating (Y) to thatwithout the coating (Y₀) as follows:Internal transmission corresponds to Y/Y₀×100 percent.

For the sake of convenience in the following transmission means theinternal transmission.

Using the software WinCol Version 1.2 supplied by the instrumentmanufacturer the colour evaluation of the transmission spectra was done.Here the CIE tristimulus values (standard colour values) X, Y and Z ofthe transmission spectrum in the wavelength range 380 nm to 780 nm arecalculated in accordance with ASTM 308-94a and DIN 503. From thestandard colour values the CIELAB coordinates L*, a* and b* arecalculated in accordance with ASTM 308-94a and DIN 5033.

EXAMPLES Example 1

Silver nanowires (AgNW) were synthesized using the polyol synthesis asdescribed for example in WO-A-2012/022332. 50 g of the obtained mixturewere mixed with 130 mL of acetone. The mixture was stirred for 30 minThe supernatant solution was discarded and a precipitate is obtained.

The precipitate was mixed with 20 g of water and shaken. The mixture isthen centrifuged (2500 rpm/20 min) The supernatant is again discarded.The mixing with water, shaking, centrifugation and sedimentation isrepeated four times.

Example 2

Formulation Clevios PH 1000 with silver nanowires for transparentconductive coatings are prepared. 2.77 g silver nanowires (2.7% silvercontent gravimetrically, 75 mg silver) were mixed with 5.71 g of water,7.85 g Clevios PH 1000 (86 mg PEDOT/PSS, Heraeus Precious Metals GmbH &Co. K G, Leverkusen), 0.755 g dimethylsulfoxide (DMSO, ACS reagent,Sigma Aldrich, Munich) and 50 μL Triton X100 (Sigma Aldrich, Munich).The formulation was coated on Melinex 506 films (Pütz GmbH+Co. Folien KG. Taunusstein) using a 6 μm wet-film thickness doctor blade (Erichsen KHand Coater 620). Coatings were dried for 5 min at 120° C.

Example 3

Coated films from Example 2 were cut into pieces measuring approximately5×10 cm. The lower half of the stripes were dipped into different waterbased etching solutions for 2 min, subsequently rinsed in a water bathfor 1 min and dried for 5 min at 120° C. The surface resistivity wasmeasured before and after treatment by the four-point probe technique.The results are summarized in Table 1.

TABLE 1 Etching results Surface resistance Surface resistance Untreatedafter treatment Etchant [Ω/square] [Ω/square] Water 84 102 KMnO₄ [1%] 88n.d. KMnO₄ [0.1%] 79 5663 KMnO₄ [0.01%] 86 1595 HNO₃ [10%] 95 109 CuCl₂[7%] 91 834 H₂O₂ [10%] 113 1100 Dichloroisocyanuric 91 n.d. acid [10%]n.d. non detectable (>1 × 10⁸ Ω/square)

The color coordinates in the L*a*b coordinates system were determined onthe etched and untreated pieces of the films. The differences (ΔL, Δa*and Δb*) are shown in table 2.

TABLE 2 L*a*b values Etchant ΔL* Δa* Δb* Water 0.05 0 0.03 KMnO₄ [1%]2.45 0.74 2.72 KMnO₄ [0.1%] 1.44 0.4 1.8 KMnO₄ [0.01%] 1.03 0.32 1.31HNO₃ [10%] 0.1 0 0.07 CuCl₂ [7%] 0.16 0.1 0.29 H₂O₂ [10%] 0.34 0.1 0.26Dichloroisocyanuric 0.21 0.18 0.05 acid [10%]

Furthermore, the transmission (Y D65/10° value) of the etched anduntreated pieces of the films was measured. The results are shown intable 3.

TABLE 3 transmission transmission transmission Etchant untreated aftertreatment Water 97.7 97.6 KMnO₄ [1%] 97.15 91.07 KMnO₄ [0.1%] 97.3293.49 KMnO₄ [0.01%] 97.61 94.73 HNO₃ [10%] 97.3 97.5 CuCl₂ [7%] 97.397.6 H₂O₂ [10%] 97.4 98.3 Dichloroisocyanuric 97.4 97.9 acid [10%]

As can be seen from the results shown in tables 1, 2 and 3, usingorganic compound capable of releasing chlorine, such asDichloroisocyanuric acid, for etching conductive layers containingsilver nanowires leads to a remarkable reduction of the surfaceresistance (see table 1) without significantly affecting the opticalproperties of the etched areas (see tables 2 and 3). Using the etchingcompounds of the prior art for etching conductive layers comprisingsilver nanowires, such as CuCl₂, HNO₃, H₂O₂ or KMnO₄, either leads to asignificant deterioration of the optical properties (as can be seen forKMnO₄ in tables 2 and 3) or to a comparatively low reduction of thesurface resistance (as can be seen for CuCl₂, HNO₃ and H₂O₂ in table 1).

Example 4

Films that have been etched with a 10% solution of dichloroisocyanuricacid were stored in a climate cabinet at 85° C. and 85% humidity for 2or 4 days and the surface resistivity was measured again. For allsamples the surface resistivity of the etched part was not detectable(>1×10⁸ Ω/square).

The invention claimed is:
 1. A method for producing a layer structure, comprising the process steps: i) coating a substrate with a composition comprising silver nanowires, a sulfonated polymer, a conductive polymer and a solvent, wherein the conductive polymer is a polythiophene; ii) partially removing the solvent, thereby obtaining a substrate that is coated with an electrically conductive layer, the electrically conductive layer comprising the silver nanowires, the sulfonated polymer and the conductive polymer; and iii) bringing into contact selected areas of the electrically conductive layer with an etching composition, thereby reducing the conductivity of the electrically conductive layer in these selected areas, wherein the etching composition comprises an organic compound capable of releasing chlorine, bromine or iodine, a compound containing hypochloride, a compound containing hypobromide or a mixture of at least two of these compounds; wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 10 times greater than the surface resistance of the layer provided in process step ii); and wherein the color difference (ΔE) between the selected areas that have been brought into contact with the etching composition in step iii) and the electrically conductive layer provided in step ii) is at most 4.5.
 2. The method according to claim 1, wherein the silver nanowires in the composition used in process step i) have a length of from 1 μm to 200 μm, a diameter of from 20 nm to 1,300 nm and an aspect ratio (length/diameter) of at least
 5. 3. The method according to claim 1, wherein the silver nanowires in the composition used in process step i) are obtained by a process comprising the process steps: a) providing a reaction mixture comprising a polyol, an organic chemical which is adsorbed on to a silver surface, a chemical which forms a halide and/or one which forms a pseudohalide, wherein the chemical which forms a halide is a salt of one of the halides Cl⁻, Br⁻ and/or I⁻ and wherein the chemical which forms a pseudohalide is a salt of one of the pseudohalides SCN⁻, CN⁻, OCN⁻ and/or CNO⁻, a chemical which forms a redox pair, chosen from the group consisting of bromine, iodine, vanadium and mixtures thereof, and a silver salt, and b) heating the reaction mixture to a temperature of at least 100° C.
 4. The method according to claim 1, wherein the sulfonated polymer in the composition used in process step i) is polystyrene sulfonic acid (PSS).
 5. The method according to claim 1, wherein the conductive polymer is present in the form of a complex formed from the polythiophene and the sulfonated polymer.
 6. The method according to claim 5, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT) and is present in the form of a PEDOT/PSS-complex.
 7. The method according to claim 1, wherein the organic compound capable of releasing chlorine, bromine or iodine comprises at least one structural element (II)

wherein Hal is a halogen selected from the group consisting of chlorine, bromine and iodine, Y is selected from N, S and P, and X₁ and X₂ can be the same or different and each denote respectively a halogen, a carbon atom or a sulphur atom, and wherein one or more further atoms can optionally be bonded to X₁ and X₂.
 8. The method according to claim 7, wherein the organic compound capable of releasing chlorine or bromine comprises at least two structural elements (II) in which Hal denotes a chlorine atom or a bromine atom and Y denotes nitrogen, wherein the at least two structural elements (II) can optionally be different from one another.
 9. The method according to claim 8, wherein the organic compound capable of releasing chlorine or bromine comprises the structural element (III)

in which a chlorine atom or a bromine atom is bonded to at least two of the nitrogen atoms.
 10. The method according to claim 9, wherein the organic compound capable of releasing chlorine or bromine is sodium dichloroisocyanurate, sodium dibromoisocyanurate, tribromoisocyanuric acid or trichloroisocyanuric acid.
 11. The method according to claim 1, wherein the etching composition used in process step iii) comprises the organic compound capable of releasing chlorine, bromine or iodine, the compound containing hypochloride, the compound containing hypobromide or the mixture of at least two of these compounds in a concentration in a range from 0.01 to 50 wt.-%, relative to the total weight of the etching composition.
 12. The method according to claim 1, wherein the bringing into contact of the electrically conductive layer with the etching composition is performed by dipping the electrically conductive layer into the etching composition or by printing the electrically conductive layer with the etching composition.
 13. The method according to claim 1, wherein the method comprises as a further process step: iv) washing the electrically conductive layer brought into contact with the etching composition.
 14. The method of claim 1, wherein step iii) is performed without affecting the optical appearance of the selected areas.
 15. The method of claim 1, wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 100 times greater than the surface resistance of the layer provided in process step ii).
 16. The method of claim 1, wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 1,000 times greater than the surface resistance of the layer provided in process step ii).
 17. The method of claim 1, wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 10,000 times greater than the surface resistance of the layer provided in process step ii).
 18. The method of claim 1, wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 100,000 times greater than the surface resistance of the layer provided in process step ii).
 19. The method of claim 1, wherein the color difference (ΔE) between the selected areas that have been brought into contact with the etching composition in step iii) and the electrically conductive layer provided in step ii) is at most 3.0.
 20. The method of claim 1, wherein the color difference (ΔE) between the selected areas that have been brought into contact with the etching composition in step iii) and the electrically conductive layer provided in step ii) is at most 1.5. 